1. Field of the Invention
The present invention relates to rubber compositions for tire treads, and more particularly rubber compositions for tire treads which provide excellent braking performance and driving stability not only on general roads with pavement but also on wet road surfaces of motor race circuits.
2. Description of the Related Art
In recent years, as automobiles become capable of running at higher speeds, requirements imposed on their tire properties have become increasingly severe. Among such properties are performances of tires in operation at a high speed on a wet road surface. In order to improve tire properties including braking performance and driving stability on wet surfaces at high speeds, it is possible to take measures including enhancing the power for gripping the road surface, improving cornering characteristics by increasing the block rigidity of tire tread patterns and thereby resisting deformation at the time of cornering, and preventing a hydroplaning phenomenon by prohibiting deformation of grooves formed in tire treads so that water held in the grooves is discharged smoothly.
Conventionally, gripping power was enhanced by incorporating silica to high-styrene SBR, which has excellent mechanical characteristics.
Silica-containing rubber compositions for tire treads can improve gripping power in a low temperature range of 15xc2x0 C. or less. However, they have the drawback that they cannot exhibit successful gripping power on wet road surfaces or on semi-wet (damp) road surfaces in a high temperature range of 15xc2x0 C. or more, in which cooling effect by water is small.
In addition, if a great amount of silica is incorporated into a rubber composition, silica particles grind an oxide coating of the inner surface of a mixer during kneading, and then rubber components adhere to the flakes thus produced to reduce operating efficiency.
In view of the foregoing, an object of the present invention is to provide a rubber composition for tire treads which enhances gripping power on wet and semi-wet road surfaces which are not only in a low temperature range but also in a high temperature range, and which enhances operating efficiency during manufacture of the composition.
Accordingly, a first aspect of the present invention is a rubber composition for tire treads comprising a rubber component containing at least 70 parts by weight of a styrene-butadiene rubber whose styrene content is 20 to 60% (the unit of the styrene content is % by weight, in any sentences in the specification and claims); and Comprising, based on 100 parts by weight of the rubber component,
5 to 150 parts by weight of a powdery inorganic compound represented by the following formula (I) and having a particle size from 0.01 to 10 xcexcm:
mM1xe2x80xa2xSiOyxe2x80xa2zH2Oxe2x80x83xe2x80x83(I)
in which M1 is at least one selected from the group consisting of Al, Mg, Ti, and Ca; any oxide of any one of the metals; or any hydroxide of any one of the metals; and m, x, y and z are integers from 1 to 5, 0 to 10, 2 to 5, and 0 to 10, respectively, and
5 to 170 parts by weight of carbon black having a nitrogen adsorption specific area of 80 to 280 m2/g so that the total amount of the powdery inorganic compound and the carbon black, falls in the range of 70 to 200 parts by weight,
wherein the amount of an extract obtained by extracting the rubber composition after being vulcanized from acetone and chloroform is 30 to 270 parts by weight, based on 100 parts by weight of the rubber components.
A preferable embodiment of the first aspect of the present invention is a rubber composition for tire treads comprising a rubber component containing at least 70 parts by weight of a styrene-butadiene rubber whose styrene content is 30 to 45%; and comprising, based on 100 parts by weight of the rubber components,
15 to 120 parts by weight of a powdery inorganic compound represented by the following formula (I) and having a particle size from 0.05 to 5 xcexcm:
mM1xe2x80xa2xSiOyxe2x80xa2zH2Oxe2x80x83xe2x80x83(I)
in which M1 is at least one selected from the group consisting of Al, Mg, Ti, and Ca; any oxide of any one of the metals; or any hydroxide of any one of the metals; and m, x, y, and z are integers from 1 to 5, 0 to 10, 2 to 5, and 0 to 10, respectively, and
15 to 140 parts by weight of carbon black having a nitrogen adsorption specific area of 80 to 280 m2/g so that the total amount of the powdery inorganic compound and the carbon black falls in the range of 70 to 180 parts by weight, and
5 to 40 parts by weight of at least one of a C9 aromatic petroleum resin and an alkylphenol resin,
wherein the amount of an extract obtained by extracting the rubber composition after being vulcanized from acetone and chloroform is 30 to 200 parts by weight, based on 100 parts by weight of the rubber component.
A second aspect of the present invention is a rubber composition for tire treads comprising a rubber component containing at least 70 parts by weight of a styrene-butadiene rubber whose styrene content is 20 to 60%; and comprising, based on 100 parts by weight of the rubber component,
5 to 150 parts by weight of a powdery inorganic compound represented by the following formula (I) and having a particle size from 0.01 to 10 xcexcm:
mM1xe2x80xa2xSiOyxe2x80xa2zH2Oxe2x80x83xe2x80x83(I)
in which M1 is at least one selected from the group consisting of Al, Mg, Ti, and Ca; any oxide of any one of the metals; or any hydroxide of any one of the metals; and m, x, y, and z are integers from 1 to 5, 0 to 10, 2 to 5, and 0 to 10, respectively,
5 to 100 parts by weight of silica having a nitrogen adsorption specific area of 130 to 280 m2/g, and
5 to 170 parts by weight of carbon black having a nitrogen adsorption specific area of 80 to 280 m2/g so that the total amount of the powdery inorganic compound and the silica falls in the range of 80 to 250 parts by weight,
wherein the amount of an extract obtained by extracting the rubber composition after being vulcanized from acetone and chloroform is 30 to 270 parts by weight, based on 100 parts by weight of the rubber component.
A preferable embodiment of the second aspect of the present invention is a rubber composition for tire treads comprising a rubber component containing at least 70 parts by weight of a styrene-butadiene rubber whose styrene content is 30 to 45%; and comprising, based on 100 parts by weight of the rubber component,
15 to 120 parts by weight of a powdery inorganic compound represented by the following formula (I) having a particle size from 0.05 to 5 xcexcm:
mM1xcexa8xSiOyxe2x80xa2zH2Oxe2x80x83xe2x80x83(I)
in which M1 is at least one selected from the group consisting of Al, Mg, Ti, and Ca; any oxide of any one of the metals; or any hydroxide of any one of the metals; and m, x, y, and z are integers from 1 to 5, 0 to 10, 2 to 5, and 0 to 10, respectively,
30 to 100 parts by weight of silica having a nitrogen adsorption specific area of 130 to 280 m2/g,
15 to 140 parts by weight of carbon black having a nitrogen adsorption specific area of 80 to 280 m2/g so that the total amount of the powdery inorganic compound and the silica falls in the range of 100 to 230 parts by weight,
5 to 40 parts by weight of at least one of a C9 aromatic petroleum resin and an alkylphenol resin, and, based on the amount by weight of the silica,
3 to 20 percents by weight of a silane coupling agent,
wherein the amount of an extract obtained by extracting the rubber composition after being vulcanized from acetone and chloroform is 30 to 200 parts by weight, based on 100 parts by weight of the rubber component.
The above and other objects, features, and advantages of the present invention will become apparent from the following description.